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SurveillanceSummariesGiardiasis SurveillanceUnited States, 1992–1997U.S. DEPARTMENT OF HEALTH & HUMAN SERVICES
Centers for Disease Control and Prevention (CDC)
Continuing Medical Education for U.S. Physicians and NursesAugust 11, 2000
The MMWR series of publications is published by the Epidemiology Program Office,Centers for Disease Control and Prevention (CDC), U.S. Department of Health andHuman Services, Atlanta, GA 30333.
Centers for Disease Control and Prevention.CDC Surveillance Sum-
maries, August 11, 2000. MMWR 2000;49(No. SS-7).
[Author(s)]. [Title of particular article]. In: CDC Surveillance Sum-
maries, August 11, 2000. MMWR 2000;49(No. SS-7):[inclusive pagenumbers].
Centers for Disease Control and Prevention . Jeffrey P. Koplan, M.D., M.P.H.
The production of this report as an MMWR serial publication was coordinated in
Epidemiology Program Office . Barbara R. Holloway, M.P.H.
Office of Scientific and Health Communications . John W. Ward, M.D.
CDC Surveillance Summaries . Suzanne M. Hewitt, M.P.A.
Use of trade names and commercial sources is for identification only and does notimply endorsement by the U.S. Department of Health and Human Services.
References to non-CDC sites on the Internet are provided as a service to MMWRreaders and do not constitute or imply endorsement of these organizations or theirprograms by CDC or the U.S. Department of Health and Human Services. CDC is notresponsible for the content of pages found at these sites.Vol. 49 / No. SS-7ContentsAugust 11, 2000Reports Published in CDC Surveillance Summaries Since January 1, 1990ResponsibleCIO/Agency*Most Recent Report
State-Specific Prevalence of Selected Health
Contribution of Birth Defects to Infant Mortality
Family Planning Services at Title X Clinics
*Abbreviations
Agency for Toxic Substances and Disease Registry
National Center for Chronic Disease Prevention and Health Promotion
National Center for Environmental Health and Injury Control
National Center for HIV, STD, and TB Prevention
National Center for Injury Prevention and Control
National Institute for Occupational Safety and Health
Vol. 49 / No. SS-7Reports Published in CDC Surveillance Summaries Since January 1, 1990 — ContinuedResponsibleCIO/Agency*Most Recent Report
Infant Mortality (see also National Infant Mortality;
Neisseria gonorrhoeae, Antimicrobial Resistance in NCPS
August 11, 2000Vol. 49 / No. SS-7Giardiasis Surveillance — United States, 1992–1997
1Epidemic Intelligence Service, Epidemiology Program Office, CDC
2Division of Parasitic Diseases, National Center for Infectious Diseases, CDC
AbstractProblem/Condition: Giardia intestinalis, the organism that causes the gastrointestinalillness giardiasis, is the most commonly diagnosed intestinal parasite in public healthlaboratories in the United States. In 1992, the Council of State and TerritorialEpidemiologists assigned giardiasis an event code that enabled states to beginvoluntarily reporting surveillance data on giardiasis to CDC.Reporting Period: This report includes data that were reported from January 1992through December 1997.Description of the System: The National Giardiasis Surveillance System includes dataabout reported cases of giardiasis from participating states. Because most states werealready collecting data on occurrence of giardiasis, the assignment of an event code togiardiasis has allowed voluntary reporting of these data to CDC via the NationalElectronic Telecommunications System for Surveillance.Results: Since 1992, the number of states reporting cases of giardiasis to CDC has risenfrom 23 to 43. The annual number of giardiasis cases reported has ranged from 12,793in 1992 to 27,778 in 1996. In 1997, cases per 100,000 state population ranged from 0.9to 42.3, with 10 states reporting >20.0 cases per 100,000 population and a nationalaverage of 9.5 cases per 100,000 population. In 1997, New York State, including NewYork City, reported the highest number of cases (3,673, or 20.3 cases per 100,000population), accounting for 14.5% of cases nationally; however, Vermont reported thehighest incidence rate in 1997 (42.3 cases per 100,000 population). Both states haveactive surveillance systems in place for giardiasis. Cases have an approximately equalsex distribution. Nationally, rates were the highest among children aged 0–5 years,followed closely by persons aged 31–40 years. In these two age groups, most caseswere reported during late summer and early fall — an indication that transmissionoccurred during the summer.Interpretation: This report documents the first nationwide look at epidemiologicparameters and disease burden estimates for giardiasis in the United States.Transmission occurs in all major geographic areas of the country. The seasonal peakin age-specific case reports coincides with the summer recreational water season andmight reflect the heavy use by young children of communal swimming venues (e.g.,lakes, rivers, swimming pools, and water parks) — a finding consistent with Giardia’slow infectious dose, the high prevalence of diaper-aged children in swimming venues,the extended periods of cyst shedding that can occur, and Giardia’s environmentalresistance. Estimates based on state surveillance data indicate that as many as 2.5million cases of giardiasis occur annually in the United States.August 11, 2000Public Health Action: Giardiasis surveillance provides data to educate public healthpractitioners and health-care providers about the scope and magnitude of giardiasis inthe United States. These data can be used to establish research priorities and to planfuture prevention efforts.INTRODUCTION
Giardiasis is the gastrointestinal illness caused by the flagellated protozoan Giardia
intestinalis, also known as G. lamblia or G. duodenalis. Giardia is the most commonlydiagnosed intestinal parasite in public health laboratories in the United States (1–4 ).Giardia was the most frequently identified etiologic agent of outbreaks associated withdrinking water in the United States for the years 1976–1994 (5 ).
Giardia is spread from person to person and from animals to humans through fecal-
oral transmission, has an incubation period of 3–25 days (median, 7–10 days), and hasa two-stage life cycle — trophozoite and cyst. The life cycle begins with ingested cysts,which release trophozoites (10–20 µm x 5–15 µm) in the duodenum. These trophozo-ites attach to the surface of the intestinal epithelium by using a ventral sucking disk andthen reproduce by binary fission. The trigger for encystment is unclear, but the processresults in the inactive, environmentally resistant form of Giardia — a cyst (11–14 µm x7–10 µm) that is excreted in feces (6 ).
Giardiasis occurs when cysts are ingested through person-to-person transmission
or ingestion of fecally contaminated food or water. The infectious dose is low: humanscan be infected with as few as 10 cysts (6,7 ). Persons at greatest risk of exposure toinfection are children in day care, their close contacts, men who have sex with men,backpackers and campers (via ingestion of unfiltered, untreated drinking water), travel-ers to disease-endemic areas, and persons drinking water from shallow wells (8–11 ).
Giardia is found worldwide and infects domestic and wild animals (e.g., cats, dogs,
cattle, deer, and beavers) (6,7 ). Giardiasis usually occurs sporadically, although out-breaks do occur. Waterborne outbreaks, associated with ingestion of both drinking andrecreational water (e.g., lakes, rivers, or swimming pools) (5 ), and foodborne outbreaks(12,13 ) are well documented as are person-to-person outbreaks among men who havesex with men (8 ) and among children and staff in day care centers (14 ). The relativecontribution of waterborne, foodborne, and person-to-person transmission to sporadicgiardiasis is unknown.
Clinically, Giardia produces a broad spectrum of gastrointestinal symptoms, in-
cluding one or more of the following symptoms: diarrhea, flatulence, bloating, weightloss, abdominal cramping, nausea, malabsorption, foul-smelling stools, steatorrhea,fatigue, anorexia, and chills. Although the hallmark of giardiasis is diarrhea, asymp-tomatic infections can occur (15,16 ), especially in children and in persons with priorinfections (6 ). Giardia cysts can be excreted in the stool intermittently for weeks ormonths, resulting in a protracted period of communicability (14,17,18 ).
Because infections can be asymptomatic or characterized by mild signs and symp-
toms, giardiasis is often regarded as a benign gastrointestinal illness, although chronicor debilitating giardiasis has been reported (15 ). From 1979 through 1988, an esti-mated 4,600 hospitalizations per year in the United States resulted from severe giardia-sis and its complications, resulting in an average of 23,238 days per year in the hospital
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and a mean annual incidence of 2.0 hospitalizations per 100,000 persons (15 ). Volumedepletion was reported for 33% of case-patients, and 19% of hospitalized children aged<5 years had a codiagnosis of failure to thrive (15 ).
Many effective treatment alternatives are available for patients with symptomatic
giardiasis (Table 1). Metronidazole is the treatment most often prescribed in the UnitedStates. Furazolidone is a less effective treatment option, but it is the only drug ap-proved by the U.S. Food and Drug Administration (FDA) for treatment of giardiasis inthe United States. Because furazolidone is available in liquid form, it is often used totreat children (6 ). Quinacrine, an effective and inexpensive treatment option, is notavailable from any U.S. manufacturer, although several compounding pharmacies havemade it available. Tinidazole is widely used throughout the world; however, it is notapproved for use in this country. Albendazole has been reported to be as effective asmetronidazole with fewer side effects among children aged 2–12 years (19 ). Paromo-mycin, a nonabsorbed aminoglycoside, is less effective than other agents but is usedfor treatment among pregnant women because of potential teratogenic effects of theother agents (20 ). A combination of metronidazole and quinacrine has been used totreat refractory cases (21 ).TABLE 1. Drugs for treatment of giardiasis*Drugs(listed alphabetically)Adults (nonpregnant)
100 mg by mouth 4 times a day for 7–10 days
250 mg by mouth 3 times a day for 5–7 days
500 mg (30mg/kg/day) by mouth 3 times a day for 7 days
Pregnant Women
500 mg (30 mg/kg/day) by mouth 3–4 times a day for 7 days
Children
6–8 mg/kg/day by mouth divided 3–4 times a day for 7–10 days
15 mg/kg/day by mouth divided 3 times a day for 5 days
30 mg/kg/day by mouth divided 3 times a day for 7 days
6 mg/kg/day divided 3 times a day for 5 days (maximum = 300 mg/day)
Refractory Cases
750 mg by mouth 3 times a day for 14 days
100 mg by mouth 3 times a day for 14 days
* Sources: Ortega YR, Adam RD. Giardia: overview and update. Clin Infect Dis 1997;25:545–50; Taylor GD, Wenman
WM, Tyrrell DLJ. Combined metronidazole and quinacrine hydrochloride therapy for chronic giardiasis. CMAJ1987;136:1179–80; Sanford JP, Gilbert DN, Moellering RC, Sande MA. The Sanford guide to antimicrobial therapy,27th edition. Vienna, VA: Antimicrobial Therapy, Inc., 1997; and Anonymous. Drugs for parasitic infections. MedLett Drugs Ther 1998;40:1–12.
† Not commercially available in the United States.August 11, 2000
Despite the public health importance of giardiasis, reliable data on national inci-
dence and prevalence in the United States are not available. Estimates have been ex-trapolated from published data collected by states with active giardiasis surveillance,laboratory surveys, and waterborne-disease outbreak reports. Giardiasis is the mostfrequently reported diarrheal disease in northern New England (10 ), and from 1983through 1986, it was the most common reportable disease in Vermont (22 ). Giardiaalso was the most prevalent protozoan parasite in Arkansas during 1997 (23 ) as wellas the most commonly reported enteric pathogen in Wisconsin during the years1983–1986 (24 ).
The prevalence of Giardia in stool specimens submitted for examination ranges
from 2% to 5% in industrialized countries and from 20% to 30% in developing coun-tries, and it can be as high as 35% among children attending day care centers in theUnited States in a nonoutbreak setting (4,6 ). Before the tightening of water treatmentstandards, an estimated 25% of endemic cases of giardiasis in the United States werewaterborne (7,9 ). Furthermore, giardiasis was one of the two leading recognized eti-ologies in the 129 water-associated disease outbreaks that occurred during the years1991–1994 in the United States (7 ).
Although giardiasis reporting is required by 43 states, it is not a nationally notifiable
disease (25,26 ). In 1992, the public health importance of the disease prompted theCouncil of State and Territorial Epidemiologists to assign an event code (code 11570) togiardiasis to allow states to voluntarily transmit their reported giardiasis data to CDCvia the National Electronic Telecommunications System for Surveillance (NETSS) (27 ).State health departments collect data on giardiasis case-patients from both health-careproviders and laboratories, and the data are subsequently transmitted with notifiabledisease information to CDC via NETSS.
The purpose of the National Giardiasis Surveillance System is to estimate the dis-
ease burden in the United States and to monitor the demographic parameters (sex,age, race, ethnicity), seasonality, and geographic variation of giardiasis. This reportsummarizes national surveillance data on giardiasis for the years 1992–1997.
The diagnosis of giardiasis is made through examination of stool specimens that
are typically collected and preserved in 10% formalin, although fresh stool may also beexamined. Light microscopy can be used to visualize the parasite via wet mount, stain-ing (trichrome or iron hematoxylin), or the direct fluorescent antibody detection method(monoclonal antibodies). In addition, enzyme linked immunosorbent assay (ELISA)-based kits have been used to detect Giardia-specific antigen in stool (4,6 ).
Approximately 85% of infections can be diagnosed with a single stool specimen.
Sensitivity increases with the number of stool specimens examined, so that three speci-mens collected every other day during a 5-day period will detect approximately 90% ofinfections (28 ). In the rare occasions when infections are suspected but multiple stooltests are negative, duodenal fluid can be sampled for Giardia trophozoites. Three pro-cedures have commonly been used: the string test (Entero-test), endoscopy with upperintestinal aspiration, and endoscopy with upper intestinal biopsy (6 ). No serologic testis commercially available (4,6 ).
The National Giardiasis Surveillance System collects data on persons who have
either symptomatic or asymptomatic giardiasis, seek health care, have a positive diag-
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nostic test result, and are reported to both the state and CDC (29 ). This report repre-sents the first time that national surveillance information on giardiasis has been pub-lished and includes reports from the 43 participating states.
Since the inception of the National Giardiasis Surveillance System in 1992, the num-
ber of states voluntarily reporting cases and the number of states reporting >100 casesper year increased through 1994 and subsequently plateaued. In 1992, only 23 statesreported giardiasis cases to CDC, with only 17 states reporting >100 cases. By 1997, 43states reported giardiasis cases, with 40 of those states reporting >100 cases each.
In 1992, a total of 12,793 cases of giardiasis were reported. The number of reported
cases eventually doubled by 1994. Between 1994 and 1997, case reporting plateaued at25,389–27,778 cases reported per year, with sex distribution being approximately equal(Figure 1). In 1997, New York State, including New York City, reported the highest num-ber of cases (3,673), accounting for 14.5% of cases nationally.FIGURE 1. Giardiasis case reports, by sex* — United States, 1992–1997ts 25,000rpo 20,000 Re 15,000Year of Report
*1.0%–2.3% of case reports have no sex identification.
In 1997, cases per 100,000 population ranged from 0.9 to 42.3 in reporting states.
Vermont reported the highest incidence rate (42.3 cases per 100,000 population) (Table2). Ten states reported >20.0 cases per 100,000 population (Alaska, Colorado, Minne-sota, Nebraska, New Hampshire, New York, North Dakota, Oregon, Vermont, and Wis-consin). Seven states reported no cases to CDC in 1997 (California, Connecticut, Ken-tucky, New Jersey, North Carolina, South Carolina, and Texas) (Table 2).
A bimodal age distribution in giardiasis rates was observed. The highest rates of
giardiasis occurred among children aged 0–5 years, followed closely by persons aged31–40 years (Figure 2).August 11, 2000TABLE 2. Giardiasis case reports — United States, 1992–1997*No. case reports% of totalin 1997†populationin 1997†

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